I'm amazed you're not being held on charges honestly. You used deadly force on a man fleeing the scene. Your only defense, as I can see it, is that they were still committing armed robbery (a felony). While they were fleeing though, you no longer had the threat of deadly force against you and your right to use deadly force to protect yourself was no longer in effect.

I hope your state's laws are different than mine!

I don't think they wanted to charge me with anything considering the perp was a career criminal that had been on a robbing spree spanning 3 months prior to running into me. So I felt like I was a hero for putting an end to his spree and not killing him in the process.